US 7529059 B2
A method determines RW head radial position relative to tracks within a magnetic data disc. This involves sensing both a S-burst signal and a P-burst signal with the RW head. The S-burst signal and P-burst signal are associated with a two-burst servo pattern on the magnetic disc. The S-burst pattern has a phase that remains constant radially across tracks within the magnetic disc. The P-burst has a second phase that rotates radially across tracks within the magnetic disc. By determining a phase difference between a sensed S-burst signal and P-burst signal, it is possible to determine the RW head radial position relative to the tracks on the magnetic disc.
1. A method comprising:
sensing a first burst servo pattern on a portion of a track of a rotatable medium used for data storage, wherein the sensed first burst servo pattern is one of a plurality of first burst servo patterns that are disposed radially across the rotatable medium on each half track of each track of the rotatable medium and in which all first burst servo patterns have a same phase relationship;
sensing a second burst servo pattern on the portion of the track of the rotatable medium following the sensed first burst servo pattern, wherein the sensed second burst servo pattern is one of a plurality of second burst servo patterns in which a corresponding second burst servo pattern follows each first burst servo pattern on each half track and in which all second burst servo patterns across two adjacent tracks have different phases;
determining a phase difference between the sensed first burst servo pattern and the sensed second burst servo pattern; and
locating head radial position based on the phase difference between the sensed first burst servo pattern and the sensed second burst servo pattern.
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8. An apparatus comprising:
a sensing head;
a disk controller to control positioning of the sensing head;
a rotatable medium under control of the disk controller in which a first burst servo pattern is disposed radially across the rotatable medium on each half track of each track of the rotatable medium, wherein all first burst servo patterns across tracks of the rotatable medium have a same phase relationship, and in which a corresponding second burst servo pattern is disposed following each first burst servo pattern on each half track of the medium, wherein all second burst servo patterns across two adjacent tracks have different phases, so that a phase difference between a sensed first burst servo pattern and a corresponding sensed second burst servo pattern on a particular half track identifies radial position of the sensing head based on the phase difference between the sensed first burst servo pattern and the sensed second burst servo pattern.
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This application is a continuation of and claims priority to U.S. Patent Application having an application Ser. No. 11/405,872; filed Apr. 18, 2006; which application claims priority to U.S. Provisional Patent Application Ser. No. 60/780,974, filed Mar. 10, 2006; in which both above listed applications are incorporated by reference herein.
The present invention relates generally to determining a Read/Write (RW) head position relative to magnetic media, and more particularly, to determining the RW head position relative to magnetic media based on a phase error associated with a servo pattern.
The structure and operation of hard disk drives is generally known. Hard disk drives include, generally, a case, a hard disk having magnetically alterable properties, and a read/write mechanism including Read/Write (RW) heads operable to write data to the hard disk by locally alerting the magnetic properties of the hard disk and to read data from the hard disk by reading local magnetic properties of the hard disk. The hard disk may include multiple platters, each platter being a planar disk.
All information stored on the hard disk is recorded in tracks, which are concentric circles organized on the surface of the platters.
Since each track typically holds many thousands of bytes of data, the tracks are further divided into smaller units called sectors. This reduces the amount of space wasted by small files. Each sector holds 512 bytes of user data, plus as many as a few dozen additional bytes used for internal drive control and for error detection and correction.
Typically, these tracks and sectors are created during the low level formatting of the disk. This low level formatting process creates the physical structures (tracks, sectors, control information) on the disk. Normally, this step begins with the hard disk platters containing no information. Newer disks use many complex internal structures, including zoned bit recording to put more sectors on the outer tracks than the inner ones, and embedded servo data to control the head actuator. Newer disks also transparently map out bad sectors. Due to this complexity, all modern hard disks are low-level formatted at the factory for the life of the drive.
The ability to store and access increased amounts of data depends on the ability to accurately position the RW head relative to the data tracks. Positioning of the RW head relative to the physical structures is typically based on amplitude information of two (2) or four (4) bursts within a servo pattern. This amplitude information is subject to noise, and environmental changes. A four burst amplitude servo pattern is illustrated in
This four burst pattern does not allow all the disk space to be effectively used. This servo pattern requires unused media leaves less user data space on the media for storage. To realize additional storage availability, require higher data density is required which may result in a poor quality and production yield.
Further limitations and disadvantages of conventional and traditional RW head positioning processes and related functionality will become apparent to one of ordinary skill in the art through comparison with the present invention described herein.
The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Drawings, the Detailed Description of the Embodiments of the Invention, and the Claims. Other features and advantages of the present invention will become apparent from the following detailed description of the embodiments of the invention made with reference to the accompanying drawings.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:
Preferred embodiments of the present invention are illustrated in the FIGs., like numerals being used to refer to like and corresponding parts of the various drawings.
Embodiments of the present invention provide a system or method operable to locate and position a read-write (RW) head in order to more efficiently utilize magnetic media within a hard disk drive that substantially addresses the above-identified needs. A first embodiment of the present invention provides a method to determine RW head position relative to a track within the magnetic media. This involves sensing a two burst servo pattern. A phase difference between the two bursts is determined. This hard disk drive contains a disk controller that is able to accurately compute the RW head position and position the RW head of the hard disk drive based on phase differences between first and second sensed burst signals. By accurately positioning the RW head, the physical structures (i.e. tracks and sectors) and data therein and accessed more efficiently.
The disk controller locates and positions the RW head based on a two burst servo pattern. The disk controller locates and positions the RW head based on phase difference sensed between the two bursts. (i.e. the S-burst and the P-burst)
By positioning the RW head using phase information, the disk controller may provide a finer control of the position (i.e. location) of the RW head relative to the magnetic media. This type of positioning reduces or eliminates position errors associated with prior processes. The reduction or elimination of position errors results in a higher quality definition of physical structures (i.e. sectors and tracks) within the hard disk that may ultimately result in both lower product cost and high product yield.
Processing module 63 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. Memory module 65 may take the form of a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the Disk controller 52 implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Processing module 63 stores and executes operational instructions corresponding to at least some of the steps and/or functions illustrated with reference to
One may also observe from the phase linearization process illustrated in
Embodiments of the present invention provide the ability to accurately position the read-write head relative to the magnetic media using only two bursts per servo wedge. This reduces the space associated with the servo pattern overhead and increases the overall memory or drive capacity. Additionally, phase information is less subjected to noise and other environmental factors when compared to amplitude information. Therefore, by using phase information of the bursts instead of the amplitudes, the Servo system provides a more robust and improved tracking quality.
When the embodiments of the present invention use an “S” burst for the reference phase, the system is more robust when examining the phase change between wedge to wedge is due to spin speed variation, disk shift, Servo pattern writing accuracy and other factors. The phase cycle covers two Servo tracks, the one bit ambiguity on cylinder number where within a Gray code can be compensated with phase information. Phase burst changes to phase by one quarter cycle every half Servo track. Thus, it is easy to accurately determine the radial position of the RW head.
In summary, embodiments of the present invention provide a method operable to determine RW head radial position relative to tracks within a magnetic data disc. This involves sensing both a S-burst signal and a P-burst signal with the RW head. The S-burst signal and P-burst signal are associated with a two-burst servo pattern on the magnetic disc. The S-burst pattern has a phase that remains constant radially across tracks within the magnetic disc. The P-burst has a second phase that rotates radially across tracks within the magnetic disc. By determining a phase difference between a sensed S-burst signal and P-burst signal, it is possible to determine the RW head radial position relative to the tracks on the magnetic disc. Track information may be determined by other means such as gray coded information within SSMs.
In other embodiments this phase difference may be used to not only determine the position but also provide the ability to reposition the RW head for improved reading of data within a track. In one embodiment the P-burst phase rotates one-quarter cycle or 90° for each half track of radial displacement. However, this amount of phase rotation may be increased or decreased in order to provide improved resolution of the radial disc placement. For example, the P-burst phase may rotate only one-eighth of a cycle or 45 degrees for each half track of radial displacement. However, this amount of rotation should not be limited to these two specific examples as other amounts of rotation are possible.
In yet another embodiment a hard disk drive having a hard disk controller at least one magnetic disc may use this two-burst servo pattern in order to determine the radial position of the RW head within the disk. With this information, the disk controller may then direct how the read-write head is to be radially repositioned.
As one of average skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. As one of average skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of average skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of average skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.
Although the present invention is described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims.